The present invention relates to a sealing device for a machine for packaging products in a controlled atmosphere, such as foodstuffs in containers such as trays, pots and similar packages sealed by a film.
The packaging of foodstuffs and other products in such sealed packages is carried out on machines called xe2x80x9csealersxe2x80x9d or xe2x80x9cthermoformer-sealersxe2x80x9d, depending on whether the containers to be sealed are produced beforehand on another machine or are produced by thermoforming a thermoplastic sheet, for example, on the same machine as that on which the sealing is carried out. It is often necessary, especially when packaging foodstuffs or pharmaceutical products, for the purpose of achieving better preservation, protection and/or hygiene, to carry out the sealing under a vacuum or in a controlled atmosphere, an operation which involves extracting air and/or injecting gas.
A known and commonly used solution consists in extracting the air and/or injecting the gas via holes made on the sides of the sealing film, along the drive systems. Admittedly, this makes it possible to establish a well-controlled atmosphere in the packages, but it does entail a not insignificant loss of sealing film, the width of the latter having to be substantially greater than that of the containers to be sealed.
Other solutions proposed hitherto for this purpose (see, for example, documents U.S. Pat. Nos. 4,162,599, 4,624,099, 5,271,207 and WO 96/09210) are complicated and expensive, and yet are not entirely satisfactory. In particular, they do not allow satisfactory sealing of the enclosure created around the container to be sealed, especially at the air extraction and/or purge-gas injection system, between the sealing film and the container to be sealed.
From another standpoint, it has not hitherto been possible to completely fill, right to the edges, containers intended to be sealed insofar as the filling takes place at a station located upstream of the sealing station and that the filled container not yet sealed is transferred from the filling station to the sealing station, an operation which involves a movement causing the formation of a wave on the surface of the product contained in the container. This is the reason why hitherto containers have only been partly filled, so that the wave which forms during transfer does not allow the product to spill out of the container or reach or sully the upper edge of the container, something which would prevent the sealing film from being welded to the container.
The subject of the present invention is a sealing device for a sealed-container packaging machine, which device, while being of particularly simple and reliable structure, ensures perfect leaktightness of the enclosure in which the welding of the sealing film to the container takes place, thus making it possible to create, in the sealed container, a better controlled atmosphere than hitherto.
The subject of the invention is also a sealing device for a sealed-container packaging machine, which allows the containers to be completely filled without the product contained in the container carrying the risk of sullying the upper edge of the container and of compromising the welding of the sealing film to the container.
The sealing device, forming the subject of the invention, is intended for a machine for packaging products under a controlled atmosphere in containers such as trays, pots and similar containers sealed with a film. This device comprises a top part forming a bell provided with a welding head and a bottom part forming a pan. The bottom part receives at least one container to be sealed and interacts with the top part so as to define, around the container to be sealed, an enclosure in which the continuous sealing film brought beforehand onto the container is welded to the container by the welding head of the top part. According to the invention, the top part comprises, in one wall, on the side where the sealing film is brought in, a slot through which the sealing film passes, controlled-actuation closure and immobilization means, for closing off said slot and for immobilizing the film with respect to the top part, and means for the introduction and/or extraction of fluid, emerging inside the enclosure between said slot and the bottom edge of said wall.
Said closure and immobilization means may preferably consist of an inflatable hose placed in said wall, on one side of said slot. Said inflatable hose is advantageously mounted in a hole extending in said wall over the entire width of said slot, in such a way that said slot is secant to said hole.
Said means for the introduction and/or extraction of fluid may comprise gas injection orifices, gas extraction orifices and/or orifices or spouts for filling the container at the sealing station.
Insofar as, on most sealers or thermoformers, the top part of the sealing station comprises, for the purpose of adaptation to containers of different shapes and sizes, a mounting plate on which may be attached, selectively, welding heads of different shapes and sizes and frames of different shapes and sizes, extending around the welding head, said wall, through which the slot capable of being closed off, by the controlled actuation of said closure and immobilization means, passes, advantageously forms part of a frame capable of being attached to the top part, around the welding head, instead of the usual frame.